Final answer:
Self-expression is not considered a sphere of physical activity, unlike public health, work, and health, which relate directly to physical activity and its effects on health and daily function.
Step-by-step explanation:
All of the following EXCEPT self-expression are considered spheres of physical activity. Options such as public health, work, and health directly relate to physical activity in the context of improving health outcomes, contributing to daily job functions, or maintaining individual well-being through exercise. On the other hand, self-expression can involve a wide range of activities, not all of which are related to physical activity or exercise. While physical activity can be a means for self-expression, especially in activities like dance or sports, self-expression itself is not fundamentally concerned with physical fitness or good health.